tweaks: don't bother asking ncurses for keycodes for shifted Left/Right

These modified keys have codes by default: KEY_SLEFT and KEY_SRIGHT.
It's just the shifted Up/Down keys that don't have default codes.

src/nano.c

@@ -2579,8 +2579,6 @@ int main(int argc, char **argv)
 	controldelete = get_keycode("kDC5", CONTROL_DELETE);
 	controlshiftdelete = get_keycode("kDC6", CONTROL_SHIFT_DELETE);
 
-	shiftleft = get_keycode("kLFT", SHIFT_LEFT);
-	shiftright = get_keycode("kRIT", SHIFT_RIGHT);
 	shiftup = get_keycode("kUP", SHIFT_UP);
 	shiftdown = get_keycode("kDN", SHIFT_DOWN);
 

src/nano.h

@@ -599,8 +599,8 @@ enum
 #define SHIFT_ALT_RIGHT 0x432
 #define SHIFT_ALT_UP 0x433
 #define SHIFT_ALT_DOWN 0x434
-#define SHIFT_LEFT 0x451
+//#define SHIFT_LEFT 0x451
-#define SHIFT_RIGHT 0x452
+//#define SHIFT_RIGHT 0x452
 #define SHIFT_UP 0x453
 #define SHIFT_DOWN 0x454
 #define SHIFT_HOME 0x455

src/winio.c

@@ -538,13 +538,7 @@ int parse_kbinput(WINDOW *win)
 		return CONTROL_DELETE;
 	else if (retval == controlshiftdelete)
 		return CONTROL_SHIFT_DELETE;
-	else if (retval == shiftleft) {
+	else if (retval == shiftup) {
-		shift_held = TRUE;
-		return KEY_LEFT;
-	} else if (retval == shiftright) {
-		shift_held = TRUE;
-		return KEY_RIGHT;
-	} else if (retval == shiftup) {
 		shift_held = TRUE;
 		return KEY_UP;
 	} else if (retval == shiftdown) {